Rotary well drilling system



May 19, 1942- A. l-lol i A1\1DEl=v 2,283,207

ROTARY WELL DRILLING SYSTEM Filed Nov.`l8, 1939 3 Sheets-Sheet l Aimar HOzzander INVENTOR BY gw TORNEYS May19, 1942. A. HOLLA'NDER 4 2,283,207

ROTARY WELLDRILLING SYSTEM Filed Nov. 18, 1939 5 Sheets-Sheet 2 .D FN uw: Rw

G Q Lg I Q k "5% Q LRP. 5&1 Q G Q U INVENToR ATTORNEYS AZczcZar Hollander,

'May 1'9, 194; A. HOLLAN'DER '2,283,207

ROTARY WELL DRILLING 'SYSTEM F'iled Nov. 18, 1939 3 Sheets-Sheet 5 ladclzr foiandr:

INVENTOR ATTOR NEY Patented *May' 19, 1942 2,283,207 ROTARY WELL DRILLING SYSTEM t Aladar Hollander, Angeles, Calif., assignor to Byron Jackson Co., Huntington Park, Calif., a corporation of Delaware Original application March 21, 1938, Serial No.

197,139. Divided and this application Novem ber 18, 1939,v Serial No. 305,136 f (Cl. Z55-24) 3 Claims.

This invention relates generally to well drilling by the rotary method, and more particularly Y to a system for circulating drilling iiuid in a4 well during the drilling operation.

drag. With full measure differential across the pistons, the size of cylinders is deiinitely limited at the prevailing pressures because of the pistony drag, which increases with the pressure and in l In drilling wells by the rotary method, the bit 5 proportion to the piston, diameter. Small pisis rotated by a string of hollow drill pipe sustons .necessitate high piston speeds in order to pended from the surface and through which obtain the required volume, andthe resulting drilling mud is circulated downwardly to the high velocity of abrasive fluid causes rapid abra,- bit and upwardly outside the drill pipe to the sion of cylinder liners. With the full pressure surface. The upward circulation carries the l0 differential across the pistons, any leakage rap- Vcuttings to the surface where they are sepaidly develops into high velocity jets .which cut rated from the mud prior to recirculationof the i the rubberpistous aS though a knife Were usedmud in the well. Settling pits, screens, and 2. Even with duplex pumps the discharge is separators of various types are employed to repulsating, and, at the high pressures prevailing, move the cuttings,'but complete removal thereof 15 this pulsation causes destructive vibration of is never eiected. Consequently the mud pumps the pumps, piping connections, and drill pipe. are required to handle fluid containing a con- 3. The piston rods are necessarily under comsiderable amount of abrasive material, resultpression When moving in one direction, and the ing in rapid abrasion of pump parts. length of stroke is therefore limited due to the iIt is well established that the jetting action of tendency of long rods to buckle. I the mud issuing from the bit passages has 4a 4f Pump l'od Stung boxes are exposed on one pronounced effect on the rate of penetration of side -to the drilling mud, requiring frequent the bit into the formation, and, inasmuch as the servicing of stuffing boxes and replacement of force of the j'ets is a function of the mud prespiston rods. sureat the bit, the drilling speed can be ma- 5. Because of the short stroke and small diterially augmented by maintaining a relatively ameter pistons, the number of valve actuations high mud pressure. The pressure required at Der unit of time is necessarily high, andthe the pump discharge in order to obtain the derapidity of change from extremelyhigh pressure vsirecl jettigv action depends on the length of the i to suction at each piston reversal causes pound-- drill pipe, the internal diameter of the drill pipe, ing of the valves, resulting in relatively short and the size of the mud passages in the bit. life of valves and valve seats.

Since the size of the drill pipe necessarily de- 6. When Changing 130 Smaller Size drill Pipe creases with greater depth, the mud pressure after reaching considerable depth, it is cutomat the pump must be increased greatly for deep ary to replace cylinder liners and pistons with wells. Pressures ranging from 30o lbs/sq. in. 35 ones of smaller size. in order to obtain higher for shauow depths up to 16oo1bs./sq.in.for depths pressures. This is e troublesome and expensive of around 8000 feet are typical. In the event the practice. l

drill pipe becomes stuck or the bit openings be-l Because of the excessive wear and tear on come clogged it issometimes necessary to boost pump parts as the result Voi. the above-menthe pressure to as high as 5000 lbs/sq. in. to 4o tioned`causesthe maintenance cost lsivery high. overcome this condition. The volume require- For example, the time requiredto drill an 8000- .ments are fro`m 200 to 800 gal./min. It is thus foot Well is, on an average, about 120 days; dur-V seen that the mud pumps are required to handle ing this time the mud pumps are operating a wide range of volumes of abrasive-laden fluid about 90 days. It is customaryto replace cylinat a wide range of high pressures. der liners, pistons, cylindery heads, valves, and

The only available type of pump capable of valve seats as many as 15 to 20 times in this 90 handling mud in the vo1ume and pressure ranges dey period, resulting in a replacement oost pery required is the duplex double 'acting recipro- Dun'ip for Dump Darts alone ou a Single '8000-fowl eating pump. This type of pump is, however, far Well. in the neighborhood of $3000. which, iSv from ideal for this purpose, and is used only practically the initial Cosi? of o Dumpf. because nothing more suitable is available. Of The most common sources of power Vfor mud the many defects inherent in such pumps. the. pumps are steam, electricity, and internallco .-f..H following are among the most troublesome: bustion engines. Various combinationssazoiathe:'-V

1. The pressure differential across the pistons latter two have been tried in recent yeersirnonee is the full discharge pressure; In order to avoid 0f Which are entirely Sei'iSfaofforY-A` `The? ''r-e piston leakage hp type rubber pistons are used; quire expensive and cumbersome equipment, "and: A, while they prevent leakage, the drag exerted on unless additional Speed reduotio und Speed Con* the cylinder walls. is tremendous, resulting in trol mechanism is provided. they lack there rapid wear of cylinder liners and pistons, not to quired range of flexibility Furthermore they'ii mention the energy consumed in overcoming this 6.0 lack the feature of automatic adjustment to load, and in the .event of sudden stoppage of flow of mud the pressure yis likely to rise to the bursting point before it can be relieved. To the best of my knowledge, there is not available at present a pressure relief valve capable of handling `such a situation at the prevailing pressures.

Steam is preferred by operators as a source of power for the mudpumps, chiefly because it is preferable as a drive for the drawworks and the rotary table arid is readily available. It also is more flexible' than the so-called ."power drives. The mud pumping units almost universally used at the present ,time comprise direct-acting steam-driven duplex pumps, in which the engine piston rods are connected directly tothe pump piston rods. These units, however, have several outstanding defects in addition to the defects inherent in the pumps per se, such as: n

1. A large majority of boilers used with drilling ing hydraulic motor, and is therefore properly characterized as a simplex, orsingle cylinder pump, as distinguished from a duplex, doubleacting pump. v

With the substantial equalization of pressures on opposite sides of the pistons, the sealing effect With a slightly higher pressure on. the motive rigs are designed to operate at a pressure of about i 225 lbs.,.and itis obvious that with a direct-acting failing. to utilize the adiabatic expansion of thev steam. This obviously results in low fuel emciencyand requires a boiler plant of higher steam capacityl than would otherwise be necessary.

3.. It isy customary to mount the mud pumps in close proximity to the well, whereas the boilers l are required to be set back a distance sufficient to remove the fire hazard. Consequently, long steam lines .are required from the boilers to the mud pumps, resulting in considerable heat loss.

n Withthe aforementioned defects in view, I have invented. a novel mud pumping system free 'from all such defects and having other advantages which will be set forth more in detail hereinafter. inasmuch as one of the chief causes of trouble rod to buckle.

liquid side of the pistons, any leakage across the pistons will be of clean motive liquid rather than of drilling mud, and the peripheries of the pistons will be kept washed clean. Contamination of the clean motive liquid `by drilling mud is also avoided .by this arrangement. The leakage of a small amount of clear water into the drilling mud is not obJectionable since it is nece'ssary to add make-up water to the mud from `time to time.

The elimination of several other defects of prior pumps is alsov made possible by the substantialr equalization of pressure on opposite sides of the piston. The limitation on piston diameter, imposed by the piston drag as discussed above, is

. removed and relatively large pistons and cylinders may be employed.' With increased piston area the piston speed, and consequently the fluid velocity, may be reduced while still maintaining the same output volume of mud. Reduction in fluid velocity results in additional reduction of wear on the cylinder walls. v

By the present arrangement, the piston rod is always under tension, and never under compression, making it possible to provide a long stroke such as would be impossible if the piston rod were under compression, because of the tendency of the Of equal importance is the fact that there is no stufllngA box exposed to mudthe only stufllng box is exposed to clear motive liquid on both sides.

An actual embodiment of a pump'accordingY to my invention has two coaxial cylinders each 6 feet in prior mud pumps is the existence of full pressure differential across the pistons, a principal object of this invention is to provide a mud pumping system employing a pump in which lthe pressure differential across the pistons is reduced to a minimum. 'I'his I have accomplished by the provision of a single cylinder'divided centrally by a transverse partition, forming in effect two coaxial cylinders. A piston in each cylinder is connected to opposite ends of a common piston rod extending through the partition. One cylinder contains a driving or motive liquid under pressure and drilling' mud under pressure, the two liquids being separated by the piston and the motive liquid beingunder a pressure only slightly greater than the mud pressure. The other cylinder contains spent motive liquid and suction mud on opposite sides of its piston, both of these liquids obviously being under substantially equal pressure with the motive liquid pressure slightly higher than the mud pressure.` 'I'hefmotive liquid is alternately admitted to the twocylinders, causing reciprocation of the pistons and the pumping of mud from one'cylinder while the other draws in mud.

A hydraulic pump of' -this type functions similarly to a single cylinder, double-acting pump direct-connected to a single cylinder, double-actlong and 10 inches in diameter. It will be apparent that by the provision of cylinders of this length and diameter a long, slow stroke 'is possible, resulting in relatively few reversals per minute. The number of valve actuations is proportionately reduced, and the pounding of valves on their seats as the result of rapid valve actuation is eliminated entirely.

Q A still further object o'f this invention is to provide a mud pumping system wherein the highly desirable performance characteristics of a centrifugal pump may be availed of, without subjecting the centrifugal pump to the harmful effects of the abrasive mud. The performance characteristlcs of a centrifugal pump are ideally suited to pumping drilling mud. When driven at constant speed it has no definite head or capacity, but is dependent on the resistance to flow of the pumped liquid for the establishment of any fixed head or i capacity. It has, however, a denite shut-off head for a given speed, and regardless of flow resistance it will not develop a. greater head. -It also has a denite maximum capacity at zero head for any given speed. By merely varying the pump speed or throttling the discharge, the pressure and volume can be varied through a wide range. There is no necessity of changing the size vof the mud pump liners and pistons to obtain varying pressures, as in pumps now in use. These characteristics make thecentrifugal pump ideal engine or an electric motor.

for pumping drilling mud, s o far as hydraulic performance is concerned.

However, because of the abrasive nature of drilling mud, it would not be practicable to handle the mud directly by a centrifugal pump. Replacement of worn parts would be required even more frequently than with pumps now in use. In a system in accordance with this invention, however, the volume and pressure characteristics of a centrifugal pump may be transferredto the drilling mud indirectly through the novel balancedpiston hydraulic pump, wherein the displacement of mud equals that of the clear motive liquid, and the mud pressure is always only a few` pounds less than that ofthe motive liquid.

A still further object of this invention is to provide a hydraulic mud pumping system comprising a prime mover, a centrifugal pump driven thereby and delivering clear -motive liquid, land a hydraulic mud pump actuated by the motive liquid. i

. -Another characteristic of centrifugal pumps which makes them especially well adapted to supply motive liquid for hydraulic pumps handling drilling mud vis their capability of being compoundedeither in series or in parallel, providing unusually wide pressure and volume ranges. When drilling at relatively shallow depths, a large volume of mud4 at pressures lranging from 600 to 800 lbs./sq. in. is required while at great depths a decreased volume at pressures from 1000 to 1500 lbs./sq. in. is required.l These pressure and volume requirements are obtainable with a series,- parallel multi-stage centrifugal pump, or a plurality of pumps connectible in seriesv or in parallel, while being driven at constant speed.,

A still further object of this invention is to prolpumps now in use are very ineflicient fromv a standpoint of fuel economy, chiey because steam is admitted to the cylinders during the full stroke of the pistons and the adiabatic expansion of the steam is not utilized. In the system of this in@ vention, however, the prime mover may be a steam turbine, the most efficient of any steamdriven prime mover. Or, if desired, any-other type of prime mover may be used, such as Another object of this invention is to provide v a hydraulic mud pumping system including a centrifugal pump and a hydraulic mud pump actuated by motiv liquid supplied by the centrifugal pump, the latter being driven by a steam turbine, a Diesel engine, an electric motor, or any other prime mover of high eciency. r

Other objects and advantages will become apparent from 'the following description, in conjunction with the accompanying drawings, in which Fig. l is a central'vertical longitudinal section through one form of the invention, illustrating conditions near the end of piston travel to the left;

Fig. 2 is a view similar to Fig. l, with the reversing valve in mid-position;

Fig. 3 is a view similar to Figs. 1 and 2, with the reversing valve completely reversed and the stroke of the pistons to the right begun;

Fig. 4 is a central horizontal longitudinal section through 'a slightly modified form of the invention; l

a Diesel Fig. 5 is a transversesection taken substantialpumping system installed at a well being drilled.

`Referring to Figs. 1 to3 ofthe drawings, a hollowbase plate I serves the-.dual purpose of supporting the pump and of providing a suction reservoir for fluid to be pump'ed.- Inasmuch as the pump is particularly adapted to handle drilling mud, the pumped uid will for convenience be referred to hereinafter as mud. A centrally disposed mud s'uction inlet 2 connects the interior of the hollow base with the source vof mud, such as the mud pit located adjacent a well being drilled. Mud suction connections 3 and 3' at-*the ends of the base I lead from the reservoir to the outer ends of the pump cylinders.

Secured in coaxial relation on opposite sides of `a central body 4 is a pair of cylinders 5 and" 5',

Mud valve heads 6 and 6 on the outer ends of the cylinders contain valves controlling the infiowof suction mud and the outflow of discharge mud.

the valve heads also serving as supporting connections between the outer-ends of the cylinders and the hollow base. cylinders are pistons 'I and vl', slidably mounted on the opposite ends of a common piston rod B. The extent of outward movement `of the pistons relative to the piston rod is limited by collars 9 and 9' formed von the ends of the piston. rod and engageable by the piston. Inward movement of the pistons on the rod is limited by engagement of the pistons with collars I0 and I0 secured to the piston rod. Springs II and II' interposed between the pistons and collars 9 and 9' yieldably urge the pistons inwardly. The collars 9 and 9' are slidable in bores in the pistons 1,1' in fluid-,tight relation thereto, and are in effect pistons, preventing leakage of fluid from one side to the other of the pistons 1, 1.

The central body 4 constitutes a valve chamber for motive liquid, hereinafter referred to as water for convenience, although it will be understood that any other suitable liquid may be employed. Water under suitable high operating pressure is admitted from a suitable source to the valve chamber through a water inlet I2, the spent water returning to the source through an outlet ated by a pivoted lever'I5 operably connected to r a plunger 20 reciprocable in a longitudinally Aextending bore in the central body and disposed in the path of the collars I0 and I 0' to be engaged by one of. the latter at the end of each stroke.

The valve I4 alternately admits high pressure Water from the inlet I2 to passages I6 and I 6 leading respectively to cylinders 5 and 5. When one of the passages I6 or I6 is connected to inlet I2, the other passage is in communication with outlet I3 to. vent its respective cylinder, except for a ybrief interval during reversal of the stroke,

, as will be explained hereinafter.

The mud valve head 6 at the outer end of cylinder 5 contains an yinwardly opening mud section valve I1 controlling communication between suction connection 3 and cylinder 5, and an outwardly opening mud discharge valve I8 cornmunicating with a discharge nozzle I9. Valve head ii'A on cylinder 5 is equipped with similar valves Il and I8 and discharge nozzle I9. The discharge nozzles are adapted to be connected Reciprocable within thev to a common discharge pipe for delivery of mud to the point of use. y

The mode of operation of thepump is as follows: Water or other liquid under pressure is supplied to the inlet I2 from a suitable source, preferably a centrifugal pump. When the valve i4 is in the position shown in Fig. 1, the pressure water enters cylinder 5 through passage I6, moving piston 1 to the left and forcing mud out through the discharge valve Il and nozzle i9. The pressure of the water will exceed by only a slight amount the pressure of the discharge mud, the piston speed depending on the back pressure imposed on the discharge mud. If the power pump is a centrifugal pump, it will be understood by` those familiar withy the operating'characteristics of this type of pump that the pressure developed thereby depends on the resistance to flow, and the slower the piston speed the higher the pressure developed, up to the shutoff head of the particular pum-p.

At the same time that piston 1 is pumping mud out of cylinder 5, piston I is also moved to the left, forcing spent motive liquid out of cylinder 5 through passage I6' and outlet il, and drawing mud into the cylinder to the rear of the piston from the suction reservoir through suction connection 3' and valve i1'.

During this time the high discharge mud pressure is exerted against the left end 9 of piston rod 8, while the other end thereof 9' is exposed to mud at suction pressure. Consequ ntly the spring Il will be compressed by relative moveil', however, exerts initial force greater than that necessary to force spent water out of cylinder 5', and spring Il' will remain extended as shown in Fig. l. l

As the pistons approach the left ends of the cylinders, collar I' engages the plunger 20 and gradually moves it to the left, thus shifting valves I4 to the right. The spacing of the valves Il is so related to the distance between passages I6 and I6 that passage I6' is opened to admit high pressure water to cylinder before passage I6 is closed to high pressure water. In the central position of the valve, as shown in Fig. 2, high pressure water is admitted to both cylinders momentarily, thus moving both pistons outwardly and building up pressure on the mud in both cylinders.

The equalization of the pressures acting on the opposite ends of the piston rod 8 causes the latter to move further to the left until the compression of the springs II and Il' is equalized. This movement of the piston rod causes the valve I4 to be shifted to its extreme right-hand position, fully opening the passage I8' to high pressure water and closing passage I6 to high pressure water and establishing communication between the latter passage and the outlet I3. Both pistons then move to the right, forcing mud un-` der pressure from cylinder S'and drawing mud into cylinder 5.

It lwill be 'evident that during the brief interval when pressure fluid is being admitted to both vment between piston 1 and rod 8. The spring cylinders, both pistons arepumping mud and a continuous flow thereof is thus provided. The flow of pressure liquid into the cylinders is also continuous, thus preventing waterV hammer. Both of these conditions are made possible by the oating piston arrangement.

The above described arrangement also eliminates the possibility of the reversing valve stalling on dead center, by providing a positive forcel which acts on the valve to complete the reversal thereof.

Referring now to Figs. 4 and 5, a modied reversing valve assembly is disclosed. It will be observed that with the pivoted lever valve-actuating means shown in Figs. 1 to 3 it is necessary that the reversing valve be reciprocable longitudinally of the main cylinders. In the form shown in Figs. 4 and 5, however, the valve is reciprocable transversely of the main cylinders. This is made possible by utilizing a compound rack and pinion arrangement. The central body, main cylinders, pistons and mud valves of this form of the invention are substantially identical with those shown in Figs. 1 to 3, and hence will not be described in connection with 'this form. A plunger 3l, corresponding to the plunger 20 ofl Figs. 1 to 3, is provided with rack teeth 32 along the central portion of one side thereof. Teeth 32 mesh with teeth on an elongated pinion 33 journaled on a vertical axis in the central body. As shown in Fig. 5, the plunger 3| engages the pinion 33 adjacent its lower, end.

and the toothed portion of the pinion extends a substantial distance along the pinion shaft. Spaced above the plunger 3l and extending at right angles thereto and also at right anglesto the pinion @33 is a valve `stem 35 having rack teeth 35 along the central portion of one side thereof meshing with the teeth on pinion 33. It will be apparent that reciprocation of the plunger 3l will cause oscillation of pinion 33 about its axis, which in turn will cause reciprocation of valve stem l5. i

Formed on the valve stem 35 is a pair of spaced valves 36, 36', corresponding to valves Il of Figs. 1 to 3, the valves being spaced relative to the parts so as to provide for admission of high pressure water to both cylinders simultaneously for a brief interval during reversal of the valve.

The valve arrangement of Figs. 4 and 5 has one advantage overthat of Figs. 1 to 3, in that by the transverse disposition of the valve the longitudinal dimension of the central body maybe reduced, being independent of the length of the valve assembly. Both valve' assemblies are of relatively simple construction. with aminimum of moving parts subject to wear.

From th'e foregoing description, it will be apto above, the floating piston arrangement makes it possible to actuate the reversing valve directly by the piston rod without any danger of the valve stalling in dead center-a defect inherent in directly actuated reversing valves for hydraulically operated devices.

The substantial balancing of the pressures on opposite sides of the pistons is an outstanding characteristic of this pump, reducing to a minimum the piston drag andthe consequent wear on cylinder walls. The piston rod is always under tension, and never under compression, making possible a long stroke without the danger of the piston` rod buckling. The piston rod stuffing box is exposed only to clear water and never to abrasive-laden mud. thus eliminating the necessity of frequent servicing of the stuilng box and replacement of the piston rod. Other advantages will be apparent to those familiarb with the problems encountered in the pumping of drilling mud.

In Fig. 6 is shown a schematic layout of the hydraulic mud pumping system at a Well being drilled. The well derrick floor is shown at 4|, the rotary table at 42, the' draw-works at 43, and a conventional steam drilling engine at 44.I The battery of boilers 45 are shown set back from the well in a customary manner, and connected by a steam line 46 to the drilling engine 44; a second steam line 41 supplies steam to the boiler feed water pumps 48. Thus far the lay- 15 out follows conventional practice.

`A steam turbine 5|, located adjacent the boilers, is supplied with steam through an extension 52 of the steam line 41, and is direct-connected steady flow and at steady pressure, comprising a centrifugal pump; driving means therefor; and

means for impressing on said abrasive drilling mud the pressure and vvolume characteristics of said centrifugal pump while protecting the latter from the deleterious elect of direct contact of the drilling mud therewith, said means comprising a cylinder and a movable partition in the cylinder dividing the latter into a drilling mud compartment and a motive liquid compartment; fluid connections from the drilling mud source to said drilling mud compartment and from the latterto said drill string; a source of clear, nonabrasive motive liquid having no deleterious effect on said centrifugal pump, and iiuid connections from said last-named source to the centrifugal pump and from the latter to the motive liquid to a centrifugal pump 53. This pump is a multistage centrifugal pump having a series-parallel hook-up, whereby the pump is divided into tw o halves, the stages of the two halves being capable of being compounded either in series, for high pressure, or in parallel, for lower pressure and greater volume. A water supply line 54 leading from a tank 55 is connected to the inlets 56 and 51 of the two halves of the pump, the inlet 51 being provided with a shutoff valve 58. Outlets and 6l for the respective halves merge into a 30 common discharge pipe 62. A cross-over 63 having a valve 64 is provided between outlet 60 and inlet 51, and a valve 65 is provided between outlet 60 and the common discharge pipe 62. When valves 58 and 65 are open and valve 64 is closed, 35

the two halves of the pump -are connected in parallel, each having an inlet and an outlet, and delivering a relatively large amount of water atV relatively low pressure. When valves 58 and 65 are closed and valve 64 is opened, the discharge from the first half enters the intake of the second half, and in the two halves are connected in series, delivering a relatively small amount of water at relatively high pressure.

compartment of said cylinder; whereby the pressure and volume characteristics of the centrifugal pump are indirectly irnpressedon the drilling mud through the inter ediacy of the motive liquid, and admixture of the drilling mud and motiveY liquid lare substantially prevented by the movable partition in' said cylinder.

2. In a well drilling system, in combination with a drilling rig: a mud pumping system for supplying abrasive drilling mud under pressure to the well, comprising a prime mover; a centrifugal pump driven thereby; a hydraulically actuated mud pump comprising a cylinder yand a piston reciprocable in said cylinder and dividing the 'latter into a -drilling mud compartment and a motive liquid compartment; a source of abrasive drilling mud, suction connections from said source `to said drilling mud compartment and discharge connections from the latter to the well; a

source of clear. non-abrasive liquid vhaving no deleterious effect on the centrifugal pump, suction connections from said last-named source to 0 said centrifugal pump and discharge connections The common discharge line 62 extends to the 45 hydraulic mud pump 10, and a return line 1I leads from the mud pump to the tank 55. A v

water line 12 extends from the tank to the boiler feed water pumps. A mud suction line 13 extends from the usual mud pit 14 to the suction inlet oi' the mud pump, and a mud discharge line 15 leads from the pump to the usual connection to the drill pipe (not shown);

The foregoing illustrates one type of installation, adapted for use at a steam-operated rig. It will be understood that ifpreferred any other desired type of prime mover may be employed, such asa Diesel engine or an electric motor. y

Although the invention has been explained by describing in detail 'a particular embodiment thereof,`it is to be understood that many departures can be made from the specific construction shown without departing from the invention which is to Abe limited only to the extent set forth in the appended claims. This application is a division of my copending yapplication Serial No. 197,139, filed March' 21, 1938, for Pumping apparatus.

I claim: l

l. In a well drilling system, in combination from the latter to the motive vliquid compartment of said mud pump; the piston of said mud pump being freely movable in its cyclinder to discharge drilling mud from the mud pump in response to delivery of motive liquid thereto from said centrifugal pump. and the opposed pressure areas oi' said piston being approximately equal, whereby the pressure and volume characteristicsof the discharged drilling mud are determined by and are approximately equal to the pressure and volume characteristics of the motive liquid supplied by said centrifugal pump.

pumping system for delivering abrasive drilling mud from said source to the drill string in a driving said centrifugal pump.

3. In a well drilling system, the combination with a drilling rig, of a hydraulically actuated mud pump having a suction pipe connected to a source of supply of drilling mud and a discharge pipe connected to the drill stem; said mud pump comprising a cylinder and a piston reciprocable in said cylinder and dividing the latter into a drilling mud. compartment'and a motive liquid compartment, the opposed pressure areas of said piston being approximately. equal whereby the pressure and volume characteristics'of the drilling mud discharged from the pump are deter-f mined by andy are approximately equal to the pressure and volume characteristics of the motive liquid supplied to the pump; and a source df motive liquid under pressure for actuating said pump, comprising a centrifugal pump having fluid connections with said mud pump for delivering motive liquid thereto in a steady ow and at steady pressure. and a prime mover for Y ALADAR HOLLANDER. 

